Confocal microscopes are known in which a punctiform light source is imaged onto an object, or a transferred circular and rotatable structural element located in a plane conjugated with the object field, with for example holes, grid lines or any other structures (spinning disk) is imaged onto the object and the fluorescent light reflected on the object or caused by the illumination falls onto the structural element again on the return path. Due to the reflecting patterned partially transmitting layer located on the structural element, the structural element acts as a beam splitter. Typically this layer is produced by metal vaporization, for example using chromium, silver, gold or aluminum. The metal layer is then highly reflective, whereas the gaps in the structure are highly transmitting.
If not only the transmitted light is used again for the imaging, the objective consists of guiding the reflected beam through the imaging module. For this purpose, according to the solutions of the prior art, the structural element is placed into the intermediate image plane at a sufficient angle with respect to the optical axis of the microscope system so that the reflected beam can be relayed separately from the transmitted beam. Furthermore the structural element can be oriented with respect to the optical axis so that disruptive reflections in the system are avoided.
A substantial disadvantage of the obliquely arranged structural element is that the structure imaged onto the object is also imaged obliquely, that is to say the object plane and the plane of the structural element are at an angle relative to one another. In the object space the resulting angle between these planes is dependent upon the magnification effected by the microscope optics. In this case the effect is that the structure in the object field does not act uniformly and differs as a function of the imaging scale.
A further disadvantage is that, depending upon the magnitude of the angle, the oblique position of the structural element of the depth of field of the imaging no longer gives the effect of the imaged structure for the entire object field, but only for a part of the object field for which the structural element is still located in the depth of field of the optical system. As a result of this it is not the object plane but a plane located at an angle thereto which is imaged. One side-effect is the lateral change in magnification over the image field, from image edge to image edge, or a trapezoid effect.
In DE 195 11 937 A1 an arrangement is described in which a structural element located vertically in the beam path produces a disruptive reflection. This reflection is not used as useful light. In this case the structural element is at an angle in the beam path which causes the reflection to be directed at a solid angle which does not contribute to the detected signal. Furthermore the solution includes the arrangement of a pair of prisms, wherein one prism lies along the beam path before the structural element and one prism is disposed after the structural element.
A disadvantage of this arrangement is that the reflected beam cannot be used further, since the prisms are disposed too close to the structural element, so that the reflected beam cannot be used further. Furthermore the prism arrangement is an integral component of the imaging system (imaging module), or of the tube unit.
A further considerable disadvantage is the imaging quality which is determined by the geometric arrangement of the prisms and is insufficient for the present application. In this case the principal errors are astigmatism and lateral chromatic aberration.
The arrangement implemented in EP 1 145 067 B1 involves a compromise in which the angle between the plane of the structural element and the intermediate image plane is chosen to be so great that, at a relatively low numerical aperture or resolving power of the entire system, the semi-field of view can be guided onto the detector without the above-mentioned effects occurring.